


The Improbable Improvement Investigation Incident

by Taba



Category: K-On!
Genre: Comedy, Content Warning: Precalculus, Gen, Other
Language: English
Status: Completed
Published: 2020-03-18
Updated: 2020-03-18
Packaged: 2021-02-28 23:48:34
Rating: General Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,779
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23195785
Author URL: https://archiveofourown.org/users/Taba/pseuds/Taba
Summary: Something is horribly wrong in the light and fluffy world of the Light Music Club: Yui’s grades have gone up, and no one knows why.
Comments: 1
Kudos: 30





	The Improbable Improvement Investigation Incident

“We have a big problem.” The normally cheery club president had a stern look on her face, almost stern enough to actually take her seriously. 

“What is it this time.” Mio didn’t sound that perturbed, really. Ritsu had previously called several ‘emergency meetings’ on topics as widely varied as the store being out of Ritsu’s favorite pencils, them not getting enough funding from the student council, how rich Mugi’s family actually was, whether Ui was a real human being and not a robot and/or goddess, and in one memorable occasion, trying to figure out if Sawa-chan actually had a boyfriend by following her around. Most of these emergency meetings had ended with nothing happening, although in fairness it was a different kind of nothing than the normal fare.

“And why can’t we involve Yui?” Mugi asked. Ritsu had specifically called the meeting at a time where Yui wouldn’t be there, and so it was just the three of them. Azusa couldn’t make it because she was actually studying, a concept foreign enough to most of the Light Music Club that Mio had felt that it was best to actively avoid distracting her. 

“Yui is the problem at hand!” Ritsu declared dramatically. 

Mio raised an eyebrow, and Mugi gasped. When no follow up seemed forthcoming, the two started running through possibilities:

“... Did she break something?”

“Is she fomenting a secret rebellion against your power?” Mugi was running a completely different race than Mio, it seemed. She might have even been running backwards.

“Did she go back and eat more cake while we weren’t looking?”

“Or was she abducted and replaced with a doppelganger?” 

“Or is she in danger of failing and having to go to remedial classes again?”

“No! And that’s exactly the problem!” Ritsu interjected at that last guess. “Her grades have been getting better!”

“Like, without us showing up at her house for a cram session?”

“Exactly!” Ritsu said. “It’d be one thing if we were doing that since Mio’s good at teaching, but it’s a whole nother thing for her grades to just go up like that.” The aforementioned girl blushed a bit at that compliment, something which Ritsu missed but Mugi noted very carefully. 

“So it might be the doppelganger after all...” Mio said, recovering almost seamlessly. “Well, if it isn’t, wouldn’t that be a good thing?”

“But we’re supposed to have solidarity as members of the C crew! My lieutenant should be right beside me at all times.” 

“Even as the ship goes down?” Mio asked.

“Especially as the ship goes down!” Ritsu had an aura of pride about her as she said it. “That’s how the saying goes, after all.” 

“... If you say so.” Mio said, dubious about the prospect. Mentally, she revised her idea to all go to the same college to be a little less selective.

“Alright, then what are we going to do?” Mugi asked, sounding far too into the idea of being detectives. 

“Don’t worry, I have a Plan.” 

* * *

Ritsu’s first step of her Plan was uncharacteristically normal, at least by their standards. The newly formed Light Music Club Special Investigative Division found themselves outside the Hirasawa residence, carefully peering around a nearby hedge for no particular reason. Sneakily, and thus drawing far more attention than they would otherwise, the three of them snuck up to the door. One careful look around, and then… Ritsu just rang the doorbell normally. 

“Was all this necessary?” Mio asked as they waited around.

Mugi nodded, finger held out in front of her lips, then pointed at Yui’s elderly neighbor who was watching them with more than a little amusement. When she noticed she had been spotted, she gave the trio a little wave. Mio immediately tried to shrink behind a nearby plant, muttering "If I can't see her she can't see me" under her breath.

“Hello? Oh, hi!” Thankfully, it wasn’t Yui who answered the door, but her sister Ui. None of the intrepid Special Investigative Division had any idea what they would have done if their target had responded instead, but that question would never need to be answered. 

They still needed to answer Ui, though, and so Ritsu took the lead. “Hey, Ui-chan. Is Yui at home? We wanted to hang out.”

“Ah, uhh… she’s, uh, out… doing errands?” Ui’s normally cheery expression took on a strained quality as she shifted back and forth. 

“Ah, she’s buying groceries?” 

Ui nodded just a little too quickly to be natural. “Yeah. Groceries. Yeah, the groceries for tonight’s dinner. I hope she doesn’t buy marshmallows for the hot pot like last time.”

"When will she be back, though?"

"I don't know, because she tends to get distracted easily. A- at the grocery store, there's a lot of sweets, so… yeah..." 

"Yeah, she can definitely get like that." Ritsu said in commiseration. She then pointed at the shoe rack behind them, which was a little more full than usual. "Hey, is someone over?" 

"Oh! Yeah, Azusa is here… And Jun! We're just hanging out, that's all." Ui continued fidgeting in place. 

“Ah, okay, I'll leave you to that. Tell Yui we wanted to see her, okay?” Ritsu waved, and Mio and Mugi followed suit.

“Alright, okay, see you later!” Ui bowed almost deeply enough to obscure her sweat drops, and then quickly closed the door on the three of them. 

Ritsu immediately turned to the other two, and pumped her fist. “Got her. The game is a foot.” 

Mio blinked. "What do feet have to do with anything?"

* * *

One more sneaking excursion on the way out saw Mio, Mugi, and Ritsu safe and (mostly) undiscovered at a nearby burger joint, going over what they’d learned.

“Look, her programming clearly was messing up! There’s something going on with Yui, for sure.” Mugi said excitedly. 

“Programming or no programming, she definitely was sweating there. Hey, you all remember her trying to act, right?” Ritsu said, thinking. “She was really bad at that, too.”

“That’s how we concluded she had to be an angel instead of a demon, because a demon would be great at lying.” 

“Exactly, Lieutenant Akiyama.” The newly appointed Investigator General folded her arms together. “So, she’s got to be in on it, right? There’s no way Yui would do anything without telling Ui at least a little.”

“Sure, but we still can’t figure out what that ‘it’ is just off that.” Mio sighed. “What else are we going to do?”

“We should talk to Azusa-chan! She’s probably the closest to Yui, after all.” Mugi had a certain look of confidence in her eyes as she said that. 

“Are we sure that’s a good idea? If we’re too pushy, she might let it slip, you know?”

“I think Ritsu is right. If Azusa was ever able to actually refuse Yui, would those tackle hugs ever happen?” 

"... Probably not?" She complained and complained about it when Yui wasn't around, but Azusa's gripes with Yui's affectionate nature tended to disappear as soon as she was hugged. 

"Yeah, so I still don't think we can get her involved," Mio said. "Yui will get all close to her, and then Azusa will fold."

"It could work the other way too, though… Eh, forget it. Still too risky." Ritsu shrugged. Their kouhai was likely to refuse to cooperate just on principle, honestly. She could already hear Azusa in her mind, talking about how they were being silly and that they should really focus on learning their new pieces.

"So now what?" Mugi asked.

"Let's see..."

* * *

Mio and Ritsu waited anxiously inside the control room as one by one, the screens in front of them flickered wildly. In front of them, Mugi was typing up a veritable storm, fingers flying over two separate keyboards in front of them, pulling up all sorts of various windows. 

“Mugi! The target’s close to detecting you!” Mio shouted. Indeed, one of the screens had started blinking yellow in warning. Heeding this, Mugi focused all of her attention on that particular one, characters flying across the screen. 

“It’s no use! They’re launching a counterattack already.” Ritsu took off her comically large glasses. “Get ready...” 

Klaxon sirens were blaring over the loudspeakers now, and despite Mugi’s best efforts the yellow quickly became red. 

“It’s the firewall!” Ritsu shouted.

The monitor flashed bright red, and then burst into flame. Higher and higher the flame rose, expanding and spreading out into a veritable tidal wave. Screen after screen was engulfed, sparking helplessly as the plastic around it melted into useless goo. Mugi was typing even faster, switching her focus between monitors in the span of mere seconds, but nothing seemed to be stopping it. 

"Ritsu." Mio said, shaking a little but remaining strong in spite of that. "We have to do it now!" 

"I know." Ritsu gave one long breath, then flipped open a DO NOT OPEN case, revealing a bright blue button. Dramatically, she brought a fist down on it. "Release MegaTON!" 

With a great mechanical rumble, the back wall slid open, releasing a veritable tidal wave of water. Ritsu and Mio quickly scrambled into the glass bunker that had just emerged from the ground behind them; Mugi was still typing away frantically, but just in time a barrier grew to surround her and the computers as well. 

The firewall's advance was slowed, but wasn't stopped by the torrent of water, and even seemed to be still growing - until a massive turtle emerged from the new gap in the wall. The Tactical Offensive Network let out a cry, then shot a ferocious jet of water from its mouth, blasting back the firewall. Slowly but steadily, the fire died down under the torrent of high pressure water, the defensive measures failing under the might of MegaTON. 

The two Investigative Club members not preoccupied by hacking let out a cheer as the turtle lazily swam back into its resting spot, the water being pumped back into the back room as well. Several of the melted monitors were sparking due to the water in the circuitry, but the rest were protected and thus were unimpeded from hacking.

With the firewall gone, Mugi was almost completely unimpeded, and in a short amount of time she grinned. "We're in," she said. Mio and Ritsu ran up to the front, peering at the screens all glowing green. With one click, files began to fill the screen, lines connecting every which way. 

Finally, one central box emerged, the core from which all the other lines radiated out from. Mugi slowly moved her mouse to the box, and looked back at the other two. They nodded, and the hacker opened it, laying bare the contents of Yui's phone for them to see - 

* * *

"I really don't think that's how it works." Mio crossed her arms. "For starters, the monitors aren't the actual computers, so destroying them wouldn't do anything, and a firewall isn't an actual wall - wait, that's not the biggest issue. We're not going to hack into Yui's phone."

"Aww, come on! Mugi's probably got some kind of control room like that, right?"

"Mmm… I don't think so?" Mugi seemed to genuinely be thinking about it, which said a lot about the absurdity of her everyday life. "We don't really do much with phones."

"Well..." Ritsu took a sip of her soda, looking thoughtful. In truth, steps 2 through n of her Plan pretty much amounted to "improvise", but they were musicians and thus were theoretically used to that. "In that case, we could just do it the old fashioned way?"

"Like, just grab her phone while she's not paying attention?" Mio asked, somewhat incredulously. 

"No, I mean like, following her like we did with Sawa-chan. We aren't thieves." 

"But we are hackers?"

"Yeah, hacking is way cooler than mere theft." Ritsu nodded sagely at that, although Mio didn't look convinced. Nevertheless, she let the topic slide, grabbing the last of the fries. "But yeah, we should just follow her. When should we do it?"

"Well, we have a test coming up, right? Therefore, right about now should be when any suspicious things happen," Mugi pointed out.

"Yeah," Ritsu said, a serious look in her eyes. "We just need to be subtle about it..."

* * *

"Hey, Yui, are you ready for the test next week?" Ritsu asked. 

Mio nearly spat out her tea, but just managed to hold it back. Mugi was looking as collected as always, but even she couldn't help but glance sideways back at Ritsu.

"Huh? Test?" Yui answered, fork halfway to her mouth with a big heaping of cake. Next to her, Azusa sighed, but didn't comment. 

"Yeah, the math test we have next Monday? You know, the one that Saotome-sensei keeps reminding us about?"

"Ehhh… I dunno?" Yui looked at Ritsu, confusion clear in her eyes. "Wait, Ricchan, is this test like a big deal?" All of a sudden, confusion switched to worry. 

"I don't know, are polynomial long division and the reasonable root theorem big deals to you?" Ritsu leaned in, grinning.

"Rational root." Mio whispered loudly in correction.

Ritsu didn't react outwardly, but did poke at Mio's foot under the table with her own to get her to stop. If Yui noticed their under-the-table scuffle, she didn't give any sign of it; she was sneakily perceptive for someone who spent most of her brainpower thinking about sweets, but at the moment she was currently thinking about calculus. "Well… Oh! Is that the potato theorem?"

"Huh?" Ritsu asked, puzzled.

"The one with the P and the Q, right? It's a potato because it's a P root, and then you have to unwrap the FOIL to get back to the original." Yui mimed unwrapping a potato and then biting into it in demonstration.

Ritsu blinked once, then twice, then turned to Mio and Mugi in puzzlement. Mio looked just as stumped, but after a moment Mugi's eyes lit up in understanding. "Ah, because after you find the root, you have to do the division, which is like undoing the distribution!" she said excitedly. "That's a good name." 

"... I guess, but that's not really part of the theorem..." Mio sighed. "Well, if you can remember it, it's good enough." 

"Wow..." Ritsu said in amazement. Her shocked face then turned to dismay. "Wait, I don't know that! I'm screwed!" Quickly, she bowed down in front of Yui. "Oh master, please reveal your secrets to your humble disciple."

"Eh? Secret? A-" Yui suddenly shifted tracks, picking up an accent out of nowhere. "Anyone can do it! Multiply, divide, it's all in the mind. Jooooo!" She struck a karate pose as she cried out. 

"Master!" Ritsu bowed again, then shot back up again. "I still have no idea what you mean. Why wouldn't math be in your mind?" 

As Ritsu and Yui's conversation devolved into a manzai sketch, Mugi turned to Azusa. "How was yesterday?"

Azusa blinked. "Yesterday? Oh, was it you at the door?" Mugi nodded, and gestured at Azusa to continue. "Ah, I see - wait, hold on..." The younger girl flipped open her phone and tapped away for a bit. In the meantime, Ritsu and Yui had shifted towards naming random math things from the book, Yui demonstrating a far better handle on things than she had previously with the caveat of getting precisely none of the names correct. 

"Sorry about that," Azusa apologized. 

"Oh, it's no problem." Mugi waved her hand in forgiveness. "Go on?"

"Yeah, it was fine. We were just hanging out. Y- uh, you know, celebrating the end of testing for the foreseeable future." The normally well-spoken Azusa had a rare misstep in her speech, but thankfully for her Ritsu wasn't there to pounce on her for it.

"It's that time of year, isn't it..." Mio sighed deeply. "We've got our own issues on that end," she said, pointing a thumb at Yui and Ritsu. The former had just completely stumped the latter with her knowledge of "the squeezy sandwich theorem", which was still the closest Yui had gotten to actually remembering the correct name of a mathematical concept.

Azusa, having finished up with her own cake, cleared her throat to get their attention. "Maybe we should practice instead," she said dryly. "It sounds like Yui-senpai will be fine."

"Yeah!" Yui said, Gitah having almost magically appeared in her hands. "Come on, we have to learn our new song!"

"Sweet Bitter Beauty Song won't go anywhere - " Mio started, and then reconsidered. "Well, if we can actually practice some, let's at least take this moment to do so..." Her voice took on a little long-suffering tone. 

Ritsu spun around, shocked at the betrayal. "Mio!" Ritsu shouted. "Come on, you gotta let me find out the secret method! It sounds even better than Hex the Third!" And, came the unspoken addition, maybe Yui would let the secret slip if they talked about it more. 

"How about you just use the regular methods that we already talked about? I don't think it's going to work." Mio replied to both spoken and unspoken statements. Ritsu sighed, then nodded, heading over to her drum set. When she passed Yui and Azusa, though, she winked at Mugi and Mio. Progress, she mouthed over at them. 

Wait, are you ready for the test? Mugi mouthed back. Ritsu opened her mouth again, considered it again, and then slumped down in defeat. She turned back to Mio, and silently made a plea for help - well, more silently, since they were already not making noise, but this time Ritsu didn't even open her mouth in lieu of looking hopefully at Mio. Sighing, her childhood friend nodded, mentally booking another late night sleepover cram session. Ritsu cheered at that, and Mugi's eyes shone.

"... Are we going to start?" Azusa asked, looking back at their silent comedy routine. 

The three of them sheepishly went back to their instruments, Mio clearing her throat and Ritsu chuckling self-consciously. Forgetting about Yui's grades just for a moment, Ritsu raised her drumsticks. "A one, a two, a one two three four!"

* * *

"Ritsu, you almost gave it away," Mio said. "That being said, it's definitely still just Yui, so we can rule body snatching out." 

"Nah, it's fine. Yui didn't even realize there was a test, so I don’t think she was at all thinking about that sort of thing. Besides, we're doing this the old fashioned way anyways, so there's no point.” Indeed, the Special Investigative Division was currently camping out in a nearby empty classroom, having left before Yui did with various hopefully believable excuses.

“What about Azusa-chan?” Mugi asked. 

“You heard her, she just wanted to practice.” Mio said. “Maybe you should learn from her some,” she directed at Ritsu. 

Ritsu stuck her tongue out at Mio, then went back to thinking about the mystery at hand. “So, do you think it's just Ui taking Yui's place during tests?"

“Would Ui do that for her, though?” Mugi asked. 

“Yes.” was the immediate response by both other Special Investigative Club members. Mugi nodded in understanding, then refined her question. “Would Yui let Ui do that for her?”

“I… don’t know? I don’t think she would, but she lets her do all sorts of other stuff. The mind of a Hirasawa is a mysterious place indeed.”

“The most dangerous game.” Mugi said, prominent eyebrows slanted inwards. The intent, focused look on the heiress’s gentle features had such an air of incongruity to it that Mio couldn’t help but giggle a bit at the sight.

"Shh! Here she comes!" Ritsu hissed, squashing Mio's laughter. 

The three of them very carefully peeked out as a humming Yui strolled by the door, arms outstretched and face carefree. Behind her, Azusa was keeping pace with her, sighing but with the hint of a smile on her face as well. As they turned the corner, the three aspiring sleuths followed suit, likewise tailing them down the staircase and into - 

"The library?" Ritsu whispered. Mugi nodded, and the trio slipped into the library behind them. 

Peeking out from behind a row of reference books, Mugi, Ritsu, and Mio saw the other two members of the Light Music club sit down at a table next to each other, books opened and clearly preparing to study. Dumbfounded, the Special Investigative Division looked back at each other, confusion mirrored on all of their faces. The completely reasonable idea that Yui was actually just studying had completely slipped their mind, likely because their guitarist was possibly the least reasonable person on the planet. 

As they watched, Yui was talking about something related to drinking tea while the tea was cold - it was hard enough to follow her line of thought right next to her at times; following her through several bookshelves while she was speaking quietly was almost impossible - while Azusa tried to steer the conversation back to the math at hand. The three eavesdroppers watched as Yui actually focused, tapping her mouth with the end of her pencil, then attacked the problem in front of her. Azusa merely watched her sempai without commenting, and then smiled at her when she was finished. Yui cheered, and leaned in for a hug that was swiftly denied, Azusa admonishing her to focus on studying.

"At least she's in good hands, right?" Mugi smiled. 

"Yeah… Wait, so Azusa's learning our material for Yui?" Mio asked. "That's impressive, honestly."

"When she puts her mind on something, Azusa can be really amazing, huh?" Ritsu said. They watched for a little longer as Yui solved the next couple problems. "I would never have expected Yui to just be… you know, actually reviewing."

"I feel like it's like how we bribed Yui with cake, except Azusa's bribing her with… Azusa?" Mio blinked for a moment, but she couldn't find anything wrong with the statement despite how odd it sounded. 

"It's working." Mugi pointed at the worksheet, having the best angle to actually see the page. "Her answers are all right, I think."

"Wow… Anyways, I'm still wondering how Ui fits into this whole thing, but I think that closes up this case." Ritsu sighed, stretching her arms out. "Let's go; watching them reminds me that I need to study too."

"At least something good came out of all this, then." Mio said sardonically as they retreated to give the guitarists some space to study. The Light Music Club Special Investigative Division disbanded then and there, Ritsu and Mio picking up an ages old argument about how Ritsu should stop relying on late hour Mio cramming sessions. As they bickered and as Mugi subtly egged them on, they just barely missed Azusa furtively looking around, then leaning in to give Yui a kiss.

**Author's Note:**

> Thanks to redlerred7 and @BogheadEX for various criticism and editing. 
> 
> When I came up for the idea of this fic, I had actually completely forgotten about episode 9 in season 2, which features Azusa tutoring Yui. Yeah... Consider this an alternate version of it, I guess.


End file.
